Hypers, reverse hypers, stiff deads, deads, one arm swings with dumbell, cleans, powercleans, cleans from the hang, snatch, snatch from the hang, power snatch, good mornings with straight legs, squat stance good mornings, seated good mornings, squats, all standing rowing movements, all standing pressing movements, all torso rotation work (Russian Twists, cable Woodchops etc), all oblique work (side bends, side crunches).
IMHO the best thing you can do to build your back is stop lying on it!! Get the heck of your machines and do as much work as possible standing, supporting yourself..e.g standing press, shrug, rows, cleans etc etc to build strength in the torso (abs, erectors, obliques etc). I also rejec t the isolationist approach of training the erectors seperately. Train them by utilising heavy compound lifts that involve hip and / or knee extension, not by seeking to isolate them with a machine or whatever.
Cheers, G.